Tire Size Dynamics & Calibration
Changing your tire or wheel size affects more than just aesthetics. Because your vehicle calculates speed based on tire revolutions, any change in rolling diameter will result in speedometer inaccuracies.
The 3% Safety Limit
Most automotive engineers recommend keeping any change in overall tire diameter within 3% of the original factory size. Exceeding this can interfere with anti-lock braking systems (ABS), electronic stability control, and automatic transmission shift points.
Sidewall vs. Comfort
The second number in a tire size (e.g., the '45' in 225/45R17) is the aspect ratio—the height of the sidewall as a percentage of the width. A lower aspect ratio usually provides better handling but results in a stiffer ride and less protection for your wheels against potholes.